The invention relates to a method for displaying screen elements on a reproduction screen according to the preamble of Patent claim 1.
In principle, two different methods for displaying characters are known. The first method is based on the display of characters and the second method is based on the display of pixels.
In the case of displaying characters, the character form of the individual characters is stored in a ROM table and all the character attributes such as foreground/background colour, flashing, etc. are calculated by a character generator and implemented for an entire character, an entire column or an entire screen.
Graphical images can be realized exclusively by means of a dynamically alterable character set. This means that instead of a predetermined character memory, such as a ROM, the character matrix has to be processed in a dynamic alterable manner in a RAM.
Processing of the characters using so-called window technology or vertical shifting, also called scrolling, is carried out at the character level.
A character-based screen display system generally requires little use of software, a small RAM, but, on the other hand, complex hardware and is limited in terms of its possibilities for displaying graphical elements.
In the case of the pixel-oriented mode of display, it is necessary to copy the complete character matrix line by line into a picture memory in order to generate a complete picture. All of the attributes such as foreground/background colours, flashing, etc. must be calculated by software and the arrangement of pixels must likewise be calculated in accordance with the attribute function of the associated characters, lines and/or screen.
Window technology and vertical shifting are pixel-oriented. overwriting windows or objects are usually realized using multiple-level technology.
A pixel-based screen display system generally requires very complex software, large memories, but relatively simple hardware. Whole-picture-frame pixel graphics can advantageously be created.
The invention is based on the object of specifying a method for displaying characters which has flexibility in the method of display and requires simple hardware.
This object is achieved by means of a method according to claim 1.
Advantageous developments are described in the subclaims.
In the method according to the invention, a specific number of pixels of a reproduction line are combined horizontally to form a cell. A cell may comprise for example 4, 6, 8 or 12 pixels. The number of pixels combined to form a cell is determined by a superordinate reproduction mode. The length of a cell is preferably constant, for example the length is determined by the processing width of a microprocessor that is used, and is thus 32 bits wide given a 32-bit processor. Consequently, the width can be 64 bits if a 64-bit processor is used. However, division into 2xc3x9732 bits or 4xc3x9716 bits is likewise possible.
Depending on the type of reproduction mode required, attributes such as colour, foreground and background colour, flashing or transparency display may also be contained in a cell, in addition to the pixel contents.
For line-by-line reproduction of the cells on a reproduction screen, the cells are stored in a picture memory with a respective dedicated, assigned address. The required storage capacity is equal to the requisite number of cells of the reproduction mode chosen.
The addressing of the cells in the memory takes place linearly. The number of addresses corresponds to the number of cells to be reproduced.
The linear addressing which is obtained by the inventive storage of the cells advantageously affords a reduction in hardware complexity.
Individual cell-by-cell vertical shifting is possible in a line-by-line manner. In the horizontal direction, this is done according to the cell size.
As a result of the cell-by-cell structure of e.g. objects, the latter can easily be defined by simple addressing. It is thus possible to shift or to copy entire objects or to scroll screen areas.